instream.java

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/* Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
 * 
 * This is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this software; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307,
 * USA.
 */

//
// rdr::InStream marshalls data from a buffer stored in RDR (RFB Data
// Representation).
//

abstract public class InStream {

  // check() ensures there is buffer data for at least one item of size
  // itemSize bytes.  Returns the number of items in the buffer (up to a
  // maximum of nItems).

  public final int check(int itemSize, int nItems) throws Exception {
    if (ptr + itemSize * nItems > end) {
      if (ptr + itemSize > end)
        return overrun(itemSize, nItems);

      nItems = (end - ptr) / itemSize;
    }
    return nItems;
  }

  public final void check(int itemSize) throws Exception {
    if (ptr + itemSize > end)
      overrun(itemSize, 1);
  }

  // readU/SN() methods read unsigned and signed N-bit integers.

  public final int readS8() throws Exception {
    check(1); return b[ptr++];
  }

  public final int readS16() throws Exception {
    check(2); int b0 = b[ptr++];
    int b1 = b[ptr++] & 0xff; return b0 << 8 | b1;
  }

  public final int readS32() throws Exception {
    check(4); int b0 = b[ptr++];
    int b1 = b[ptr++] & 0xff;
    int b2 = b[ptr++] & 0xff;
    int b3 = b[ptr++] & 0xff;
    return b0 << 24 | b1 << 16 | b2 << 8 | b3;
  }

  public final int readU8() throws Exception {
    return readS8() & 0xff;
  }

  public final int readU16() throws Exception {
    return readS16() & 0xffff;
  }

  public final int readU32() throws Exception {
    return readS32() & 0xffffffff;
  }

  // readString() reads a string - a U32 length followed by the data.

  public final String readString() throws Exception {
    int len = readU32();
    if (len > maxStringLength)
      throw new Exception("InStream max string length exceeded");

    char[] str = new char[len];
    int i = 0;
    while (i < len) {
      int j = i + check(1, len - i);
      while (i < j) {
	str[i++] = (char)b[ptr++];
      }
    }

    return new String(str);
  }

  // maxStringLength protects against allocating a huge buffer.  Set it
  // higher if you need longer strings.

  public static int maxStringLength = 65535;

  public final void skip(int bytes) throws Exception {
    while (bytes > 0) {
      int n = check(1, bytes);
      ptr += n;
      bytes -= n;
    }
  }

  // readBytes() reads an exact number of bytes into an array at an offset.

  public void readBytes(byte[] data, int offset, int length) throws Exception {
    int offsetEnd = offset + length;
    while (offset < offsetEnd) {
      int n = check(1, offsetEnd - offset);
      System.arraycopy(b, ptr, data, offset, n);
      ptr += n;
      offset += n;
    }
  }

  // readOpaqueN() reads a quantity "without byte-swapping".  Because java has
  // no byte-ordering, we just use big-endian.

  public final int readOpaque8() throws Exception {
    return readU8();
  }

  public final int readOpaque16() throws Exception {
    return readU16();
  }

  public final int readOpaque32() throws Exception {
    return readU32();
  }

  public final int readOpaque24A() throws Exception {
    check(3); int b0 = b[ptr++];
    int b1 = b[ptr++]; int b2 = b[ptr++];
    return b0 << 24 | b1 << 16 | b2 << 8;
  }

  public final int readOpaque24B() throws Exception {
    check(3); int b0 = b[ptr++];
    int b1 = b[ptr++]; int b2 = b[ptr++];
    return b0 << 16 | b1 << 8 | b2;
  }

  // pos() returns the position in the stream.

  abstract public int pos();

  // bytesAvailable() returns true if at least one byte can be read from the
  // stream without blocking.  i.e. if false is returned then readU8() would
  // block.

  public boolean bytesAvailable() { return end != ptr; }

  // getbuf(), getptr(), getend() and setptr() are "dirty" methods which allow
  // you to manipulate the buffer directly.  This is useful for a stream which
  // is a wrapper around an underlying stream.

  public final byte[] getbuf() { return b; }
  public final int getptr() { return ptr; }
  public final int getend() { return end; }
  public final void setptr(int p) { ptr = p; }

  // overrun() is implemented by a derived class to cope with buffer overrun.
  // It ensures there are at least itemSize bytes of buffer data.  Returns
  // the number of items in the buffer (up to a maximum of nItems).  itemSize
  // is supposed to be "small" (a few bytes).

  abstract protected int overrun(int itemSize, int nItems) throws Exception;

  protected InStream() {}
  protected byte[] b;
  protected int ptr;
  protected int end;
}